P0377
OBD-II Diagnostic Code
Severity: ModerateWhat it means
P0377 means the ECM is receiving fewer timing pulses than expected from the crankshaft or camshaft position sensor (circuit B).
This could indicate a failing sensor, damaged reluctor ring, or wiring problem.
Affected Models
- All OBD-II vehicles (1996+)
Common Causes
- Crankshaft or camshaft position sensor failing
- Damaged reluctor ring (missing teeth)
- Sensor wiring damage or interference
- ECM fault
How to Fix It
-
Inspect the crankshaft/camshaft position sensor and its wiring.
Look for damaged wires, corroded connectors, or oil contamination on the sensor.
-
Check the reluctor ring for damaged or missing teeth.
The reluctor ring is a toothed wheel that the sensor reads.
Missing teeth cause this code. -
Replace the sensor if it tests out of specification.
Sensors cost $20-$80 and are usually accessible.
Frequently Asked Questions
Can a timing sensor cause a no-start?
Yes.
If the ECM cannot determine engine position, it cannot fire the injectors or spark plugs, and the engine will not start.
What is a reluctor ring?
A reluctor ring is a toothed wheel attached to the crankshaft or camshaft.
As it spins past the sensor, the teeth create electrical pulses that tell the ECM the engine position and speed.